Dear All,
Ok, so Stu has given me a poke over on the Sonic7 facebook group about the lack of updates recently, and he's probably right!
So, firstly, to pick up on Wishful's point about rear venting, I am planning some kind of vent at the rear. I'm quite keen to make sure I bring some flow out through the rear mounted exhaust shroud I have shown previously, in order to keep this area cool, but I will definitely need something else at the rear.
My design inspirations throughout this project have been the Haarman Aventador described in my first post, with a bit of stealth fighter and batmobile thrown in (lots of this in the dash - more on that later), but another vehicle I've always loved is the venerable Back To The Future DeLorian. As yet, I haven't managed to get any design nods in to this effect, but I am half playing with the idea of a pair of time machine rear vents. What do you think? Over the top?
If not, there are still plenty of other alternatives.
Ok, so in my last major post, I was talking about the engine cover and modified scoop. So, probably hinges are the next thing to talk about. This is another area of my build where I could have used a very simple solution, and ended up spinning off into another dimension of complexity, and making a load of work for myself.
In terms of pinning the bonnet and engine cover down, the answer was always going to be Aerocatches. Nothing else was going to do!
Side note for anyone else planning on fitting Aerocatches like this - Make sure you've figured out your brake reservoir location first. I put my aerocatch supports in one of only a few possible locations, and this seriously limited my options later!
Now I could easily have put a simple pin/bolt at the other end to secure it, and knocked off early, but hell, why do that when you can design yourself a complicated gas strut assisted mechanism!
As the car is intended to be more of a show car than a racer, both mechanisms had to look the part. For the bonnet, I designed a hotrod style tilt-forward hinge, which allows the bonnet to be rotated right in front of the vehicle leaving clear access to everything below. I figured out the geometry in CAD so that it would move as desired, annd added a bracket to attach to the front grill arrangement, to hold it all in place.
After a couple of paper prototypes, I had a design that worked, and then it was onto the CNC router for cutting all the bits out.
I then bonded a frame to the underside of the bonnet, which enables me to remove the bonnet from the hinge assembly as required. This video gives the gist:
There were two problems with the first version of this hinge. Firstly, the mechanical advantage of the hinge over the bonnet wasn't as much as I had hoped, and the wind would have been likely to lift it by 10-20mm at the front before it locked out (not good!). Secondly, the two inboard knuckles of the side panels, which sit either side of the bonnet are tapered inboards, and this gripped the bonnet stopping it from moving.
These two problems required a couple of adjustments to the design. Firstly, a catch at the front to hold the bonnet down, and some fettling to the bonnet/side panels to allow a bit more slack.
Another design decision helped me with this (for a change!). I have never been a fan of the slats in the standard Sonic grill piece, and had always intended to cut them out and replace with a large flat mesh. When you cut the slats out, this makes the grill piece a lot less rigid, and allows the side panel position a bit more flexibility. Normally, this would be a bad thing, but it allowed me to squeeze out a few more millimeteres of space for the bonnet to move through.
However, having taken all the strenght out of the front grill piece, I then needed to put it back in, and that brings us back to the previously mentioned large flat mesh. This could have been a plastic formed mesh, but in order to stiffen back up the panels, I decided to go for a custom aluminium design, you guessed it, cut on the CNC (this is going to become a common theme, sorry!)
This piece also gave me a good place to fit the bonnet catch, for which I used a door slam lock I had kicking around in the garden shed. Other than a wire pull catch to release, this all works well.
As someone will inevitably mention IVA compliance of the grill mesh, I'll answer that question. As the grill cutout size is <25mm, it will need a 0.5mm radius all over to be compliant. I haven't completely figured this out yet, but I think by the time it's been given a thorough going over with the wire brush, and painted in something thick (plastidip, I'm thinking), it'll be close enough.
Right, so now onto the rear hinge. This was a lot more challenging, as the geometry at the rear is more complicated. Not only do you have the rear panel to navigate, but you've got the supports for the roll hoop to work around, and the space under the cover is quite limited.
After lots of mucking around with sliding mechanisms and other junk, I eventually settled on a compound hinge mechanism which allows the cover to travel almost vertically upwards for the first 80mm, and then starts to rotate rearwards.
A couple of versions were needed in the paper prototyping phase, trying to get something which wouldn't clash with either the inlet manifold or gear mechanims of the large ST170 motor.
Next it was back to the CNC for parts and then it just needed assembling.
Hinge figured out, again I opted for aerocatches to secure the cover down. Positioning these was much more challenging, as my upgraded roll hoop supports want to occupy the same space. Eventually I figured out a location in which I could use the hoop supports for the aerocatch support, with a simple single welded bracket.
That's all for now!